Flexible thermoplastic films are used in a variety of applications including the construction of packaging and containers, protective films and coatings, and even wall paper. Typical thermoplastic polymers types include PE, PP, and PET. PE is “polyethylene” (also known as polyethene) which is the most produced polymer in the world. In turn, PE is a thermoplastic polymer that can be found in different grades including HDPE (“high-density polyethylene”), MDPE (“medium-density polyethylene”), LLDPE (“linear low-density polyethylene”), and LDPE (“low-density polyethylene”). PP is “polypropylene.” PET is “polyethylene terephthalate.” Films can be blown or cast, and subsequently are typically stretched. Films may have one or more layers.
There is generally a need to provide visual aesthetics to PE films so products or packaging are more attractive to consumers or connote higher quality. Of course these films preferably have certain performance criteria and are cost effective. Examples of unique aesthetic effects include pearlescent, metallic-like visual effects, increased opacity, and combinations thereof. Conventional approaches to providing these visual effects to films include the use of metallic or pearlescent agents, or metallic or pearlescent inks. However, these ingredients are generally expensive and thus are cost prohibitive in many applications.
One way to characterize these pearlescent and/or metallic-like visual effects from films is by way of a Flop Index. Briefly, Flop Index is the measurement on the change in reflectance of a color as it is rotated through the range of viewing angles. A flop index of 0 indicates a solid color, while a very high flop metallic or pearlescent color may have a flop index of 15. There is a need to provide PE films that have unique aesthetic effects without, or at least minimizing, the use of expensive pearlescent/metallic agents or pearlescent/metallic inks, while preferably exhibiting desired film performance and being cost effective.
Another example of unique aesthetic effects is opacity. In some applications, film opacity connotes quality. One conventional way of providing opacity to films is the use of opacifiers such as titanium dioxide. However, there are potential drawbacks to using titanium dioxide. The ingredient is generally expensive for many applications. Moreover, it has been reported that higher levels of titanium dioxide in films may reduce sealing performance in subsequent forming or packing processes. Furthermore, high titanium dioxide loading levels tend to have titanium dioxide distribution problem in films, in which the titanium dioxide particles forms gel in film and cause so called “fish eye” defects in film. Yet further, this defect may bring in further defects in printing thereby harming the overall aesthetics of printed film. One way to characterize opacity is by ISO method 6504. There is a need to provide PE films that have improved opacity without, or at least minimizing, the use of opacifiers (such as titanium dioxide), while preferably exhibiting desired film performance properties (and do so cost effectively).
Film performance properties are another potential problem for flexible packages. To this end, flexible packages generally need to maintain their integrity and desired aesthetics throughout the supply chain, even into the consumer's home. This is particularly true in e-commerce as the supply chain is generally more demanding on flexible packages than traditional commerce channels. Good mechanical properties of the film improve flexible packages performance throughout the supply chain; and moreover, it can also allow reduction of material use and/or film thickness. However, in the case of thickness reduction, as opacity relates to thickness, a reduced thickness may pose difficulties in maintaining the desired degree of opacity. Adding more titanium dioxide to increase opacity may introduce the aforementioned problems.
Accordingly, there is a need to provide a PE film that provides unique aesthetic and/or performance properties, while more preferably eliminating, or at least minimizing, the use of expensive and/or performance inhibiting ingredients.